1. Technical Field
The present invention relates generally to a semiconductor device and a method for manufacturing the same, and more particularly to a semiconductor device including a metal line with a stable structure.
2. Related Art
In semiconductor devices, metal lines are formed in order to electrically couple devices or other conductive lines, and contact plugs are formed in order to connect lower metal lines to upper metal lines. However, the increasing degree of integration of semiconductor devices has led to a reduction in design rules. As the design rule decreases, the area available for contact holes is diminishing, so the aspect ratio of contact holes where the contact plug is formed is gradually increasing. As a result, the difficulty and importance of processes for forming the metal line and the contact plug have received an increased amount of attention.
For the metal line, aluminum (Al) and tungsten (W), each of which has excellent electric conductivity, have been widely used. Recent research has focused on using copper (Cu) as a next generation metal line material. Copper can overcome problems associated with resistor capacitor (RC) signal delay in a highly integrated high-speed operation device because copper has a relatively high electrical conductivity and low resistance. However, because it is not easy to perform a dry etching process on copper lines, a damascene process is used in order to form copper metal lines.
A method for forming a metal line with a damascene process may be performed according to the following steps. First, an interlayer insulating film is formed over a semiconductor substrate, and the interlayer insulating film is etched to form a trench. After a barrier metal layer is formed on the surface of the trench, a copper material is deposited in the trench over the barrier metal layer. Next, a chemical mechanical polishing (CMP) process is performed to form a separated copper pattern. A protective film is then formed over the pattern to prevent the upper portion of the copper pattern to physically stabilize the pattern.
In the above-described conventional semiconductor device and manufacturing method, it is difficult to form barrier metal layers over the copper pattern after separating each copper pattern by the CMP process. Although the upper portion of the copper pattern is protected by the protective film, the upper portion of the copper pattern is exposed to atmosphere during a subsequent process for forming a contact plug.